In eukaryotic organisms, transcription of the messages contained within the genome is a tightly regulated process. Transcription occurs via the coordinated action of some 40-50 distinct protein components assembled into multiple complexes that cooperate to recognize transcription start sites, perform integration of regulatory signals, and provide the enzymatic activities necessary for the synthesis of RNA transcripts. Present within each gene are control elements that dictate how and when it is transcribed. For protein-coding genes transcribed by RNA polymerase II, interactions between the core promoter and the basal machinery nucleate formation of the pre-initiation complex - an assembly containing RNA Pol II and the general transcription factors, IIA, lIB, lID, lIE, IIF and IIH, while the regulatory elements are the targets of sequence-specific DNA-binding proteins that contain domains that affect activation or repression of transcription. The cumulative effects of gene specific activators/repressors interacting with regulatory sequence elements, as well as interactions between the core promoter elements and basal machinery, dictate the strength of transcription from any particular gene. The importance of the correct regulation of gene expression cannot be overstated. Errors in transcriptional control may lead to numerous deleterious outcomes that include but are not limited to, developmental defects, uncontrolled cell proliferation, inappropriate apoptosis, and metabolic diseases. An essential component for the proper regulation of transcription is general transcription factor lID (TFIID). It is a multi-subunit complex comprised of the TATA binding protein (TBP) and 13-15 additional subunits that not only nucleates assembly of the PIC, but is also the target and transducer of numerous transcriptional regulators. We wish to understand how the multiple components of the TFIID complex work together to facilitate precisely regulated gene expression which is essential for human health. To this end we will biochemically analyze and pursue high-resolution structural studies of TFIID or its constituent subunits. We will examine interactions between TFIID and activators or chromatin and characterize intrinsic enzymatic activities present within the TFIID complex. Using several complementary biophysical techniques, we aim to gain a detailed understanding of the structure/function relationships for this central component in the RNA Pol II transcription complex.